1. Field of the Invention
The present invention relates to an apparatus and method for generating statistic traffic information that generate statistic traffic data of a road link, whose statistic traffic data is partially missing, with complement based on statistic traffic data of another road link.
2. Description of the Related Art
In general, a car navigation apparatus holds, not only map information on roads, but also statistic traffic data, which is generated based on actual traffic information regarding the past congestion statuses and link travel times in the respective sections (hereinafter, referred to as road links or merely as links) of roads. Statistic traffic data is information generated by sorting past actual traffic information (primarily link travel times) by the categories of day types, such as a weekday, a holiday, a holiday season, and the like, in each of which the traffic dynamics of a day are similar, and then averaging the sorted past actual traffic information. Thus, using statistic traffic data, a car navigation apparatus can obtain the shortest-time path to a destination averagely with the most certainty, corresponding to the day type, a time zone, or the like of a day.
Incidentally, actual traffic information to be a basis of such statistic traffic data can be obtained in Japan from VICS (registered trademark: Vehicle Information and Communication System) or a floating car. VICS is a system that online collects traffic information obtained from a vehicle sensor (hereinafter, referred to as a roadside sensor) or the like installed by a road administrator or the like, and aggregates the collected traffic information and provides the aggregated information to running vehicles and the like. A floating car is a vehicle dedicated to collecting traffic information, and actually measures, for example, the link travel time of a road through actual running on the road.
VICS cannot obtain traffic information on a road link on which a roadside sensor is not installed. On the other hand, a floating car can obtain traffic information also on a road on which VICS cannot obtain traffic information, however, a floating car can hardly obtain traffic information neither on all roads nor over all time zones. Consequently, statistic traffic data on respective road links may be missed in some time zones, for example.
For example, when a link travel time is missing even for a part of road links, it is not possible to run on these road links, and neither to accurately obtain the shortest-time path nor to accurately estimate the time required to get to a destination because an accurate link travel time is not set.
In this situation, in order to eliminate such inconvenience, a technology has been devised (for example, refer to Japanese Patent Application Laid-Open No. 2005-122461), which complements missing statistic traffic data, by referring to a connection relation, a position relation, or the like between roads. According to this technology, statistic traffic data of a road link having a missing in statistic traffic data (hereinafter, referred to as a complement target link) can be estimated (complemented) based on the statistic traffic data of another road link on the same route or that on a route in parallel, which is considered to be similar to the complement target link in traffic dynamics, in other words, to have a high degree of correlation. In this situation, the road link whose statistic traffic data is used for compliment is referred to as a complementary reference link.
FIG. 14 is a diagram showing an example of a temporal-missing link being a complement target link, and the statistic traffic data of the temporal-missing link. In FIG. 14A, the dashed line with an arrow shows a temporal-missing link (complement target link). Further, as examples of complementary reference links for the temporal-missing link, link #1 on a parallel route and link #2 on the same route are shown.
The graphs in FIGS. 14B to 14D show the variation in statistic traffic data on the respective road links (in this case, the average running speed of a vehicle on the respective road links) between 0 o'clock and 24 o'clock. The statistic traffic data of the respective links is assumed to include data such as the average running speed (corresponding to the link travel time) for each clock time of a day and the like, and if data is missing at a part of the clock times of a link, the link is referred to as a temporal-missing link.
In a conventional technology, if plural complementary reference links having statistic traffic data are present on the same route and/or a parallel route/routes, a complementary reference link is determined according to the priority order which is predetermined and fixed. For example, in a case where another link having statistic traffic data is present on the same route, the statistic traffic data of a complement target link is complemented by the use of the statistic traffic data of the link on the same route with the highest priority, while in a case where another link having statistic traffic data is absent on the same route, the statistic traffic data of a complement target link is complemented by the use of the statistic traffic data of a link on a parallel route. Further, in a case where a link having statistic traffic data is absent on none of such routes, the statistic traffic data of a complement target link is complemented by the use of the statistic traffic data of a link present in the surrounding area.